1. Field of the Invention
An apparatus dispensing a molten metal alloy bonding agent for bonding a lens block to a lens blank.
2. Description of the Prior Art
In the ophthalmic industry eyeglass lens blanks must have a method of orientating the optical axis and as well as a means of holding and driving them for the purpose of grinding, lapping and polishing the prescription into said blank lens, and edging them to achieve a proper fit into eyeglass frames when using modern optical machinery.
Low melting temperature metal alloy or similar substance is used in the ophthalmic industry for bonding or forming a block to both plastic and glass lens blanks so that they may be orientated to the optical axis and be driven to be ground, polished and edged to the proper prescription.
However, devices which have been previously described suffer from either inadequate or irregular rate of flow of the bonding substance or a cavitating of the substance from between the said lens and work block. Another problem in the area of plastic lenses is the criticality of temperature control. This is due to the fact that alloys generally melt at approximately 117.degree. Farenheit and plastic lenses become adversely affected if the temperature rises above 120 degrees Farenheit. Previously described devices sense the temperature of the vessel, not the alloy or substance proper. Since the alloy develops thermal layers in its molten state, this does not give an adequate indication of actual alloy temperature. Therefore causing plastic lenses to warp. Whereas this invention overcomes these deficiences by pressurising the vessel to provide an even constant flow in conjunction with an externally controlled valve. Secondly the thermostat device is submerged directly in the alloy or similar substance and is located at the level of the discharge orifice providing very accurate control of the temperature.